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Using experimental data from three different rogue wave supporting systems, determinism, and predictability of the underlying dynamics are evaluated with methods of nonlinear time series analysis. We included original records from the Draupner platform in the North Sea as well as time series from two optical systems in our analysis. One of the latter was measured in the infrared tail of optical fiber supercontinua, the other in the fluence profiles of multifilaments. All three data sets exhibit extreme-value statistics and exceed the significant wave height in the respective system by a factor larger than 2. Nonlinear time series analysis indicates a different degree of determinism in the systems. The optical fiber scenario is found to be driven by quantum noise whereas rogue waves emerge as a consequence of turbulence in the others. With the large number of rogue events observed in the multifilament system, we can systematically explore the predictability of such events in a turbulent system. We observe that rogue events do not necessarily appear without a warning, but are often preceded by a short phase of relative order. This surprising finding sheds some new light on the fascinating phenomenon of rogue waves.

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices.

We report on a novel method for the characterization of complex ultrashort pulses, in both amplitude and phase. This method is the straightforward extension of interferometric autocorrelation (IAC) toward frequency-resolved optical gating (FROG) and therefore displays all advantages of a collinear method for measuring few-cycle pulses. The interferometric FROG (IFROG) trace contains two independent time-frequency distributions, namely the standard second-harmonic (SH)-FROG trace and a novel non-semidefinite FROG trace, which requires new retrieval algorithms. We discuss one suitable retrieval concept that is based on an adaption of generalized projections and demonstrate it with different types of short laser pulses. The IFROG trace contains additional information that can be used for intrinsic calibration of the FROG traces. The strong redundancy of data increases the robustness of the method. IFROG is a pulse characterization method that is particularly suited for the complex sub-10-fs pulse shapes as they can arise during supercontinuum compression and gives detailed insight into the satellite structures of partly compressed continua.

Using noble gases as a nonlinear medium, it has become possible to compress energetic laser pulses into the sub-10-fs regime. Hollow fiber capillaries can serve to increase the effective interaction length of the pulses, and impressive white-light continua have been reported as a result. With demonstrated bandwidths exceeding the optical octave, this method holds the potential for generating single-cycle optical pulses. On the practical side, however, it becomes very difficult to compensate for dispersive effects and to fully exploit the enormous bandwidth. We will discuss chirped mirrors as one means for pulse compression. A further challenge lies on the characterization side. Utilizing advanced characterization schemes, we were able to demonstrate compression of a white-light continuum down to a pulse duration of 3.8 fs, which corresponds to only about 1.6 cycles at the carrier wavelength. These are the shortest pulses in the visible/near-infrared wavelength range that have ever been produced with a non-adaptive approach to dispersion compensation. Moreover, these are the shortest pulses generated using chirped mirrors, which compares favorably to previous results that were achieved with much more elaborate and lossier adaptive compression schemes.

Die Erzeugung kurzer Pulse hat in den letzten Jahren riesige Fortschritte gemacht. So ist es mittlerweile mit kommerziell erhaltlichen Lasern moglich, Pulse mit einer Halbwertsdauer von 5 bis 6 Femtosekunden (10–15 s) zu erzeugen. Bei einer Mittenwellenlange von 800 nm entspricht dieses lediglich noch etwa zwei Oszillationen des elektrischen Feldes. Mit Laserpulsen sind daher etwa 1000-mal kurzere Zeitskalen zuganglich als mit den schnellsten elektronisch hergestellten Pulsen. Ultrakurze Laserpulse stellen die schnellsten kontrollierbaren Ereignisse dar, die wir zur Verfugung haben. Nukleare Reaktionen weisen zwar Zwischenschritte auf, die u. U. noch deutlich schneller ablaufen konnen. Der Zerfall zweier Atomkerne ist jedoch zeitlich vollig unabhangig voneinander. Einen Laserpulse kann man hingegen jederzeit durch einen Strahlteilerspiegel in zwei Teilpulse aufspalten und uber unterschiedlich lange Verzogerungsstrecken laufen lassen. Das Zeitintervall zwischen diesen beiden Pulsen lasst sich dann auf Bruchteile einer Femtosekunde genau kontrollieren.

We demonstrate the generation of ultrabroad spectra in a photonic crystal fiber with a kagome-lattice transverse structure. This two-dimensional periodic photonic lattice allows for strong confinement of light without employing defect states nor using photonic bandgap guiding. Light guiding is mediated by total internal reflection in the intersections of the lattice structure, similar to tapered or micro-structured fibers. The kagome lattice structure is manufactured from a soft glass with a high nonlinearity. Using a Ti:sapphire oscillator as a pump source, we observe for the first time impressive supercontinuum generation in the guided modes of a 2D photonic lattice. Supercontinuum generation is caused by fission and radiation of higher-order solitons in the anomalous dispersion range. Our spectrum encompasses the spectral range from 200 to 1750 nm. The dependence of the continuum on coupling spot location, fiber length, and pump wavelength and power as well as on pulse duration and polarization state is investigated. Using a numerical simulation for the lattice structure, pulse propagation through this structure is theoretically studied. Our model reveals the mechanism of supercontinuuum generation in the 2D photonic structure and explains the essential experimental findings.

Dispersion compensation is a ubiquitous problem for the generation and application of ultrashort optical pulses. Early approaches to compensate for the spectral group-delay dependence in materials used prism and grating sequences for this purpose, but are limited in bandwidth. Microstructuring dielectric optical materials on the scale of the optical wavelength have developed as an alternative for inducing a desired spectral group-delay dependence. With this approach a nearly arbitrary dependence of group delay vs. wavelength can be compensated for. We will discuss different approaches to microstructured dispersion compensation, namely chirped Bragg gratings, different generations of chirped mirrors, quasi-phase-matching gratings, and arrayed-waveguide gratings. We will outline common limitations and discuss ideas to expand further the utility of these approaches.

Fortschritte auf dem Gebiet der Ultrakurzpulslaser stellen an Forschung und Technik neue Herausforderungen hinsichtlich Formung und Diagnostik komplexer Lichtfelder. Fur die Kontrolle der zeitlichen und raumlichen Spektraleigenschaften werden neuartige Optiken entwickelt. Spiegel aus Mehrfachschichten mit trickreichem Design gestatten optimale Pulskompression. Mit verbesserter SPIDER-Technik werden kurzeste Femtosekundenpulse messbar. Dispersionsarme Dunnschicht-Mikrooptiken erlauben eine Analyse von Wellenpaketen in Raum und Zeit. Mit derartigen Komponenten konnen auch optische Riesenwellen, so genannte X-Pulse, erzeugt werden.

Ultrabroadband chirped mirrors with a bandwidth of 270 THz have been manufactured using the BASIC design approach. These mirrors were used to compress the supercontinuum of cascaded hollow fibers down to 4.6 fs. The pulse duration was measured with spectral phase interferometry for direct electric-field reconstruction (SPIDER).

Inside a femtosecond laser oscillator, no coupling mechanism between the propagation speeds of the carrier and the pulse envelope exists. Therefore, the relative delay between carrier and envelope of a femtosecond oscillator will exhibit irregular fluctuations unless this jitter is actively suppressed. Both intensity and beam pointing fluctuations in the laser can introduce carrier-envelope phase changes. Based on our analysis, we are capable of reducing or avoiding certain mechanisms by proper design of the laser cavity. We use such an optimized cavity to stabilize the carrier envelope-phase to an external reference oscillator with a long-term residual jitter corresponding to only 10 attoseconds in a (100 kHz-0.01 Hz) bandwidth. This is the smallest long-term timing jitter of a femtosecond laser oscillator demonstrated to date. However, it is important to note that this stabilization was obtained with an f-to-2f heterodyne technique using additional external spectral broadening in a microstructure fiber which introduces additional carrier-envelope phase noise. We present a direct heterodyne measurement of this additional carrier-envelope phase noise due to the continuum generation process.

The speed of optoelectronic devices is normally limited by the components used on the electronic side of the device. The direct generation of short light pulses from short current pulses, for example, is limited by the speed of an electronic pulse generator or the response time of a laser diode. These electronic bandwidth limitations can be overcome by switching to indirect schemes. These schemes use optical means, whenever bandwidth is an issue. This is combined with much slower optoelectronic technology, bringing together the inherent speed of all-optical approaches and the virtues of standard optoelectronics. Apart from the generation of short pulses, we will also address their detection and characterization, their modulation, and transmission effects. These methods carry the functionality of optoelectronics from a temporal resolution of a few picoseconds well into the femtosecond range.

The output pulses of a noncollinearly phase-matched optical parametric amplifier (NOPA) are fully characterized by spectral phase interferometry for direct electric-field reconstruction (SPIDER). The SPIDER setup has been optimized for online diagnosis of tunable visible pulses with a 1 kHz repetition rate and 10–40 fs duration. The compression of the NOPA pulses by different prism sequences and commercially available chirped mirrors is investigated. For flexible phase control the end mirror of a fused-silica prism compressor has been replaced by a deformable mirror. With an evolutionary strategy guided by the spectral phase information of the SPIDER, optimal compression of the NOPA pulses to a 7.6 fs duration is achieved.

The ability to generate third-harmonic light with a broad phase-matching bandwidth at any dielectric interface offers a promising tool for the characterization of ultrafast laser pulses. Third-harmonic, interferometric frequency-resolved optical gating (TH-iFROG) exploits this nonlinearity. The TH-iFROG traces contain an abundance of information, but their complicated analytical form poses a problem for standard FROG algorithms. Here we solve the pulse retrieval problem with an evolutionary algorithm known as differential evolution. The algorithm processes a TH-iFROG trace, extracting three novel types of FROG traces that are subsequently used for pulse retrieval. The analytical forms of these FROG traces are also presented. Built-in error correction mechanisms and the large amount of redundant data make the pulse retrieval robust against measurement noise and systematic errors. The technique is demonstrated via the characterization of unamplified few-cycle pulses using a simple fused silica window as the nonlinear medium. Comparison to a reference measurement made with a commercial pulse characterization device shows excellent agreement between the measured complex electric fields.

[Portion of Introduction] In this chapter PL emission and THG by both CBD-grown and VPT-grown ZnO nanorod samples are reported. These studies clearly show that the low temperature PL emission from CBD-grown samples is both weaker in intensity and broader in terms of key feature linewidths than that from VPT-grown samples. By contrast the THG efficiency of samples grown by both the high temperature and low temperature methods are comparable to one another, and both are much larger than THG generated at a bare quartz surface. Intensity dependence measurement and interferometric frequency resolved optical gating (iFROG) measurements are used to study the THG from both sample types.[20,21] The laser pulse parameters are extracted when the pulses are subjected to both high and low chirp and our studies indicate that ZnO nanostructures grown by low temperature methods allow excellent characterization of ultrafast pulses (originally < 10 fs) and can efficiently generate THG. Consequently ZnO nanostructures grown by low temperature methods are excellent candidate materials for the technology applications discussed above.

A scheme using two pump wavelengths in the infrared and ultraviolet produces more efficient laserlike emission in air, which could benefit remote sensing applications.

The origin of a 1/f noise contribution in the long-term carrier-envelope phase (CEP) measurements of mode-locked lasers is discussed. Using two different collinear interferometers for the out-of-loop characterization of feed-forward stabilized Ti:sapphire oscillators, we suppress a possible technical origin of 1/f noise to the extent possible. Both measurements indicate a lower limit of CEP frequency noise of 1 mHz/√Hz. Investigating several possible origins of this noise floor, we find a good agreement with a quantum noise mechanism that is directly induced by intracavity-amplified spontaneous emission (ASE). These findings enable direct access to ASE noise in short-pulse oscillators, which is very hard to characterize via repetition rate fluctuations. Finally, we discuss the possible consequences for frequency-comb-based timekeeping and frequency metrology, as well as for attosecond science.

A novel variant of spectral phase interferometry for direct electric-field reconstruction (SPIDER) is introduced and experimentally demonstrated. Other than most previously demonstrated variants of SPIDER, our method is based on a third-order nonlinear optical effect, namely self-diffraction, rather than the second-order effect of sum-frequency generation. On one hand, self-diffraction (SD) substantially simplifies phase-matching capabilities for multi-octave spectra that cannot be hosted by second-order processes, given manufacturing limitations of crystal lengths in the few-micrometer range. On the other hand, however, SD SPIDER imposes an additional constraint as it effectively measures the spectral phase of a self-convolved spectrum rather than immediately measuring the fundamental phase. Reconstruction of the latter from the measured phase and the spectral amplitude of the fundamental turns out to be an ill-posed problem, which we address by a regularization approach. We discuss the numerical implementation in detail and apply it to measured data from a Ti:sapphire amplifier system. Our experimental demonstration used 40-fs pulses and a 500 $\mu$m thick BaF${}_2$ crystal to show that the SD SPIDER signal is sufficiently strong to be separable from stray light. Extrapolating these measurements to the thinnest conceivable nonlinear media, we predict that bandwidths well above two optical octaves can be measured by a suitably adapted SD SPIDER apparatus, enabling the direct characterization of pulses down to single-femtosecond pulse durations. Such characteristics appear out of range for any currently established pulse measurement technique.

Issues important for new ultrashort-pulse-measurement techniques include the generation of theoretical example traces for common pulses, validity ranges, ambiguities, coherent artifacts, device calibration sensitivity, iterative retrieval convergence, and feedback regarding measurement accuracy. Unfortunately, in the past, such issues have gone unconsidered, yielding long histories of unsatisfactory measurements. We review these issues here in the hope that future proposers of new techniques will consider them without delay, and, as an example, we address them for a relatively new technique: self-referenced spectral interferometry.

A novel adjustable adiabatic soliton compression scheme is presented, enabling a coherent pulse source with pedestal-free, few-cycle pulses in the infrared or midinfrared regime. This scheme relies on interaction of a dispersive wave and a soliton copropagating at nearly identical group velocities in a fiber with enhanced infrared transmission. The compression is achieved directly in one stage, without the necessity of an external compensation scheme. Numerical simulations are employed to demonstrate this scheme for silica and fluoride fibers, indicating ultimate limitations as well as the possibility of compression down to the single-cycle regime. Such output pulses appear to be ideally suited as seed sources for parametric amplification schemes in the midinfrared.

A new scheme for supercontinuum generation covering more than one octave and exhibiting extraordinary high coherence properties has recently been proposed [Phys. Rev. Lett. 110, 233901 (2013)]. The scheme is based on two-pulse collision at a group velocity horizon between a dispersive wave and a soliton. Here we demonstrate that the same scheme can be exploited for the generation of supercontinua encompassing the entire transparency region of fused silica, ranging from 300 to 2300nm. At this bandwidth extension, the Raman effect becomes detrimental, yet may be compensated by using a cascaded collision process. Consequently, the high degree of coherence does not degrade even in this extreme scenario.

We study multi-shot intensity-and-phase measurements of unstable trains of ultrashort pulses using spectral-phase interferometry for direct electric-field reconstruction (SPIDER), second harmonic generation (SHG) frequency-resolved optical gating (FROG), polarization gate (PG) FROG, and cross-correlation FROG (XFROG). An analytical calculation suggests that SPIDER cannot indicate instability in pulse trains well. Simulations confirm this and demonstrate that SPIDER only measures the coherent artifact. Further, the presence of instability cannot be distinguised from benign misalignment effects in SPIDER. FROG methods suggest instability by exhibiting clear disagreement between measured and retrieved traces.

A study of impulsive alignment of noble-gas dimers using picosecond laser pulses shows how to extract rotational constants and estimate polarizability anisotropies from measurements and provides detailed insight into the temporal evolution of the laser-induced alignment.

A method for improved performance of feed-forward carrier-envelope phase stabilization in amplified laser sources is presented and experimentally demonstrated. The phase stabilization scheme is applicable for a broad range of repetition rates spanning from subhertz to 100 kHz. The method relies on driving an acousto-optic frequency shifter by few-cycle transients. The phase of these transients suitably controls the grating phase of the generated index grating inside the shifter material. This approach removes beam pointing as well as amplitude noise issues observed in continuously driven feed-forward schemes. The synthesis of these gratings can be understood as the acoustic equivalent of mode-locking or acoustic frequency combs.

We present a way to actively control the appearance or destruction of rogue waves in supercontinuum generation. The scheme also allows manipulating the statistics of extreme events, independently of their generation mechanism.

Different designs of near-surface InGaSb quantum-well based SESAMs were studied in the scope of a mode-locked Tm,Ho:KLuW laser operating at 2060 nm. The laser delivered stable few picosecond pulses at 93 MHz with 150 mW output power.

We propose a novel adjustable compression scheme by two-color pumping, enabling a coherent pulse source with pedestal-free few-cycle pulses in the mid-infrared regime directly in one stage, without necessity of an external compensation scheme.

We demonstrate experimental evidence for non-instantaneous polarization decay in dielectrics. The few-femtosecond relaxation times agree favorable with solutions of the time-dependent Schrodinger equation and relate to resonances of the quantum mechanical dipole.

We demonstrate a novel scheme for improved feed-forward CEP stabilization of laser amplifiers. Synthesized acoustic few-cycle transients are used to stabilize the CEP of an optical pulse train at the amplifier repetition rate.

A novel frequency synthesis scheme and feed-forward approach is applied directly for stabilization of a sub-MHz frequency comb from a Yb:KGW CPA laser not only reduces the phase noise but also greatly simplifies the stabilization setup.

We demonstrate a novel scheme for improved feed-forward carrier-envelope phase stabilization of amplified laser sources. Electrical few-cycle pulses are used to drive an acousto-optical frequency shifter to generate bursts of CEP stabilized seed pulses at the amplifier repetition rate.

The appearance of short-lived flashes in the transverse plane of multifilaments is discussed. These flashes follow a heavy-tail fluence distribution and are intimately related to atmospheric turbulence in a gas cell.

We study multi-shot intensity-and-phase measurements of unstable trains of ultrashort pulses using two-dimensional spectral shearing interferometry (2DSI) and self-referenced spectral interferometry (SRSI) in order to identify warning signs of pulse-shape instability.

Sub-10-fs pulse generation has reached a maturity and robustness that gave rise to a rapid increase of new ultrafast applications. Some of these novel applications rely on the octave-spanning spectral width, the coherence properties, or the extremely high peak intensity of femtosecond lasers, which sets them apart from the traditional use of femtosecond lasers in ultrafast spectroscopy. In this review, we concentrate on the sub-10-fs regime and first discuss the state of the art in ultrashort pulse generation. We then report on ultrabroadband wavelength conversion schemes and dispersion control by chirped mirrors. We also review advances in pulse characterization methods, with which we can measure pulse properties with much higher accuracy than simple autocorrelation methods and which support even a bandwidth in the single-cycle regime. With the recent demonstrations of pulses with a duration of merely two optical cycles, a regime is entered where the relative phase between the carrier and the envelope of the pulse starts to play a role. We discuss methods to measure and control the carrier–envelope phase and point out applications in frequency metrology. A wealth of further novel directions and developments in femtosecond research is reviewed in this article.

We demonstrate a new technique for the design of chirped mirrors with extremely smooth dispersion characteristics over an extended ultra-broadband wavelength range. Our approach suppresses spectral dispersion oscillations, which can lead to unwanted strong spectral modulations and limit the bandwidth of mode-locked laser pulses. Dispersion oscillations are significantly reduced by coating the chirped mirror structure on the back side of a substrate, providing ideal impedance matching between coating and ambient medium. An anti-reflection coating may be added on the front side of the substrate, geometrically separated from the chirped mirror. The chirped mirror structure and the anti-reflection coating are non-interfering and can be independently designed and optimized. The separation of both coating sections provides a much better solution for the impedance-matching problems than previous approaches to chirped mirror design. We show by a theoretical analysis and numerical simulations that minimum dispersion oscillations are achieved if the index of the substrate is identical to the index of one of the coating materials and if double-chirping is used for the chirped mirror structure. Based on this analysis, we design a mirror that supports a bandwidth of 220 THz with group delay dispersion oscillations of about 2 fs2 (rms), an order-of magnitude improvement compared to previous designs of similar bandwidth. In a first experimental demonstration of back-side-coated (BASIC) mirrors, we achieve nearly transform-limited and virtually unchirped pulses of 5.8 fs duration from a Kerr-lens mode-locked Ti:sapphire laser. BASIC mirrors are particularly suited for higher-order dispersion compensation schemes. They support the extremely broad spectra of few-cycle pulses and promise to provide clean pulse shapes in this regime.

The shortest pulses periodically emitted directly from a mode-locked Ti:sapphire laser are approaching the two-optical-cycle range. In this region, the phase of the optical carrier with respect to the pulse envelope becomes important in nonlinear optical processes such as high-harmonic generation. Because there are no locking mechanisms between envelope and carrier inside a laser, their relative phase offset experiences random fluctuations. Here, we propose several novel methods to measure and to stabilize this carrier-envelope offset (CEO) phase with sub-femtosecond uncertainty. The stabilization methods are an important prerequisite for attosecond pulse generation schemes. Short and highly periodic pulses of a two-cycle laser correspond to an extremely wide frequency comb of equally spaced lines, which can be used for absolute frequency measurements. Using the proposed phase-measurement methods, it will be possible to phase-coherently link any unknown optical frequency within the comb spectrum to a primary microwave standard. Experimental studies using a sub-6-fs Ti:sapphire laser suggesting the feasibility of carrier-envelope phase control are presented.

We demonstrate femtosecond pulse operation of a soliton fiber laser at 1.06-mum wavelength. This laser makes use of a single piece of microstructure fiber that has been designed to simultaneously provide anomalous dispersion and laser gain. Using a saturable absorber mirror with deep modulation depth to initiate and sustain mode-locking, this fiber provides clean and nearly transform-limited pulses down to a pulse duration of 180 fs. To the best of our knowledge, this constitutes the first demonstration of a pure soliton fiber laser in the neodymium gain band

All optical pulse cmeasurement techniques necessarily fail in multi-shot measurements of unstable pulse trains because the measurement can only provide a single result, despite of the presence of many different pulse shapes. At the very least, however, the technique should provide a reasonable estimate of a typical pulse in the train and indicate the train's stability. While frequency-resolved optical gating (FROG, [1]) and spectral phase interferometry for direct electric-field reconstruction (SPIDER, [2]) naturally operate single-shot, multi-shot variants are very common, so it is important to understand the effects of instability on multi-shot measurements.

We show in this contribution that there is a surprising beneficial application of the noise amplification capability. Launching a pulse train with a weak sinusoidal amplitude modulation into the microstructure fiber, we observe up to 30-fold optical signal amplification of this modulation after the fiber.

Here we demonstrate a direct method to stabilize the CEP of an Yb:KGW MOP A laser system, resulting in sub-100 mrad stability. To the best of our knowledge, this value surpasses most previously measured CEP jitter for Ti:sapphire CPA systems as well as any previous attempt to stabilize Yb-based oscillator and amplifier systems. This is a crucial step in widening the utility of amplifier femtosecond Yb sources, which are easily scalable in average power and pulse energy but could not be meaningfully employed in attosecond optics until now, given the difficulty of their CEP control.

Multiphoton microscopy (MPM) is a powerful technique for high resolution imaging of biological tissues. A specially-designed chirped photonic crystal fiber (CPCF) is introduced for MPM applications. The CPCF eliminates most pulse broadening effects in a broad transmission window because its cell-size radial chirp in the cladding structure localizes the reflection of different wavelengths in different resonant layers of the cladding, similar to chirped mirrors. In contrast, traditional hollow core fiber (HCF) consists of several identical reflective layers that produce substantial higher-order dispersion. The feasibility of applying the CPCF for MPM imaging is studied. The propagation properties of the CPCF are characterized by autocorrelation traces measured with and without the CPCF, which confirms an extremely low dispersion of the CPCF. The dispersion from other optics in the MPM imaging system is further compensated by a double-folded prism pair. In the autocorrelation trace measurement, satellite peaks are observed when the length of the CPCF is short (~40 cm), which disappear when the fiber length is chosen sufficiently long. The satellite peaks appear to originate from modal dispersion. With propagation lengths above 1 m, single mode propagation can be achieved in the CPCF. The extremely low dispersion of CPCF over a wide transmission window is promising in MPM applications for the fiber delivery of femtosecond pulses, especially in sub-20fs or tunable laser illumination.

We simulate multi-shot measurements of trains of pulses with unstable shapes using SPIDER, SRSI, SHG FROG, PG FROG, and XFROG. Interferometric methods measure only the coherent artifact, while FROG methods better approximate the trains.

After introducing some fundamental concepts and definitions for carrier-envelope stabilization schemes and frequency combs, measurement schemes for the carrier-envelope phase of oscillators and amplified systems are discussed. In particular, care is taken to point out typical problems in the experimental implementation of such schemes and to indicate ways to eliminate or reduce these issues. One of these potential problems is interferometer drift, another limiting factor may be shot noise in the photo detection. After this overview on detection of the carrier-envelope phase, techniques for its active stabilization are discussed. Two major approaches are addressed: the traditional feedback technique and the recently introduced feed-forward technique. Shortcomings and advantages of either technique are carefully compared and discussed. Finally, characterization methods are discussed, including example measurements that were recently obtained with the feed-forward method. These measurements indicate the smallest residual carrier-envelope phase jitter that was ever reported.

A novel scheme for feed-forward stabilization of the carrier-envelope phase of stabilized lasers is presented, which is virtually immune against slow drift effects and beam pointing variation.

An ill-posed inverse problem of autoconvolution type is investigated. This inverse problem occurs in nonlinear optics in the context of ultrashort laser pulse characterization. The novelty of the mathematical model consists in a physically required extension of the deautoconvolution problem beyond the classical case usually discussed in literature: (i) For measurements of ultrashort laser pulses with the self-diffraction SPIDER method, a stable approximate solution of an autocovolution equation with a complex-valued kernel function is needed. (ii) The considered scenario requires complex functions both, in the solution and the rhs of the integral equation. Since, however, noisy data are available not only for amplitude and phase functions of the rhs, but also for the amplitude of the solution, the stable approximate reconstruction of the associated smooth phase function represents the main goal of the paper. An iterative regularization approach is described that is specifically adapted to the physical situation in pulse characterization, using a non-standard stopping rule for the iteration process of computing regularized solutions. Our approach is illustrated by several case studies for synthetic noisy data and physically realistic complex-valued kernel functions. Based on an example with focus on amplitude perturbations, we show that the autoconvolution equation is locally ill-posed everywhere. To date, the analytical treatment of the impact of noisy data on phase perturbations remains an open question. However, we show its influence with the help of numerical experiments. Moreover, we formulate assertions on the non-uniqueness of the complex-valued autoconvolution problem, at least for the simplified case of a constant kernel. The presented results and figures associated with case studies illustrate the ill-posedness phenomena also for the case of non-trivial complex kernel functions., Comment: 21 pages, 4 figures, accepted for publication in Inverse Problems in Science and Engineering

We consider an optical resonator containing a single mode fiber. It is driven in synchronism with its round trip time by a train of picosecond laser pulses. Due to the fiber nonlinearity and repetitive interference, complex substructure in the pulse is generated. Through variation of dispersion in the resonator, we can tune from purely temporal chaos to spatio-temporal chaos, or turbulence. Numerical simulations are compared with experimental results. Intrapulse correlations provide a measure of the degree of complexity.

A fiber ring resonator, synchronously driven by picosecond pulses, exhibits a spatiotemporal instability. A rapid modulation in the pulse envelope is spontaneously formed and evolves dynamically. This structure may be called one-dimensional optical turbulence. Single-shot detection of these structures is not viable. We report how to obtain experimental information which, when combined with numerical simulation, provides an adequate picture of the processes at work. Intrapulse correlations are studied; they reveal clear differences between dispersion of either sign. Also, they reveal the formation of soliton-like structures in the turbulent regime. A criterion is given that allows the prediction of the degree of complexity.

Pure and doped nanocrystalline ZnO films of 0.1–1.0 μm thickness were prepared by spray pyrolysis techniques. Structural properties of these thin films were investigated by electron microscopy, force microscopy, x-ray diffractometry, ellipsometry, and optical spectroscopy. Using Ti:sapphire laser pulses, the second-harmonic efficiency of the films was measured. A correlation between measured efficiency and the grain shape in the polycrystalline layers is reported. Moreover, measurements of the angular dependence of the second-harmonic intensity are indicative of the dominant role of bulk effects over surface effects for the second-harmonic generation in such films.

A synchronously pumped passive ring resonator, containing an optical fiber as a nonlinear element, is studied experimentally and numerically. Period doubling cascades up to period 32 and chaos are observed in the sequence of pulse energies emerging from the resonator. We provide evidence that beyond this instability, individual pulses encounter an instability of their temporal profile. Pulse shapes develop a substructure that may be stationary, periodic, or chaotic. The full problem thus actually involves formation of a spatiotemporal structure. In contrast to many other spatiotemporal instabilities studied in optics, we deal here with strictly one-dimensional, longitudinal spatial structure.